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60fps slowmotion at varrying speed without juddering?
Hello,
I shot some 60fps footage on my rebel 2ti. I’m editing it in a 30fps composition and I want to stretch the footage to play between half speed (200% stretch) and full speed (100%), and most importantly at varying speeds in between.
When I render the footage at speeds that aren’t exactly 100% or 200%, it gets juddery. I figured that as long as I didn’t stretch above 200% (playing greater than, or equal to, 30fps at 30fps) this wouldn’t happen.
If I export with pxl motion it looks smooth…but can’t this be avoided?
Is it just impossible to play 45fps in 30fps (as an example of 150% stretch) smoothly? I guess this would make sense because it’s not a 1:1 ratio of frames.
But I still don’t quite understand how if I’m not stretching less than 30fps in a 30fps comp, it can be juddery.
Any help would be greatly appreciated. Thanks!
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7 Replies
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How are you affecting the footage? Did you try to use time remapping?
Tudor “Ted” Jelescu
Senior VFX Artist -
Yes, I’m affecting the speed using time remaping. Right now by using the “stretch” controls and some manual tweeking in the graph editor to animate speed chamges.
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what do you have selected on the Frame Blending switch?
Tudor “Ted” Jelescu
Senior VFX Artist -
Pixel Motion. Which seems to work, but just takes so long to export.
My hope was to only have to do frame blending on a final export. For an easier workflow, what I’m doing is multiple passes of speed editing. Basically I’m composting an hour long single dolly shot that speeds up and slows down, so I’m trying to make it all one speed. To do this is is easier to do pieces at a time. So for instance once I get the speed evened out between shots, I want to adjust the overall speed.
Also my concern is with multiple exports, re-imports, and exports using pixel motion, is that there might be artifacting.
Maybe I could just precompose? But I thought you couldn’t frame blend a precomp. If the footage has frame blending enabled within the precomp, will adjusting the speed of the precomp then be properly frame blended?
Hopefully this makes sense. Long day. Thanks!
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You can time remap a pre-comp for sure, I’m not sure though of the results when it comes to frame blending. Testing some short clips would be my recommendation.
Tudor “Ted” Jelescu
Senior VFX Artist -
found some answers here: https://kb2.adobe.com/community/publishing/908/cpsid_90843.html
the main point:
“The sub pixel interpolation problem can be easily seen can be seen by viewing your comp a frame at a time while zoomed in to say 800% and observing the edge detail. This problem can be especially nasty when you’re trying to do a smooth title or credit roll that uses thin fonts. The horizontal lines that make up fine type can almost completely vanish between fields or frames if the text is moving at the wrong speed. You can test this out by creating a single pixel high horizontal line in AE and animating it from bottom to top of the frame. The only speed where you’ll get a nice solid line in every frame or field is one that is an exact multiple of the frame rate. IOW, 1 frame 1 pixel of movement, 1 frame 2 pixels of movement, and so on. Move at 1 frame and 1.33 pixels of movement and the line will appear to completely disappear then return as the line moves up the screen.”
so multiples between 100% stretch and 200% will judder. hmmm, will have to resort to some motion blurring. I think pixel motion will be the way to go…but it’s still juddery and sometimes creates artifacts.
some more resources that may be helpful to others:
https://forums.creativecow.net/thread/2/1015294
https://forums.creativecow.net/thread/202/894510thanks for your feedback Ted!
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So I might be totally wrong, in which case I would love your feedback. (I linked to another post you were commenting on, you know your stuff!)
Well…here is my logic:
The footage I’m working with are slow tracking shots of architectural exteriors that I shot with the DSLR attached to my car. I’m about 20 feet from the building, wide lens (18). When I say slow, the car is idling so an object takes about 10-20 seconds to move from the right side of the frame to the left. And the image is pretty high contrast with a good amount of detail (poles, signs, shopping carts, things with hard edges etc.)
So in the 30fps comp, when I’m time stretching at intervals that are not either 200% (60 slowed to 30) or 100% (60 playing every other frame), I’m getting judder similar sounding to the horizontal movement of a line across the fame that he talks about in the adobe post. Yes? No?
This quote sums it up: “The only speed where you’ll get a nice solid line in every frame or field is one that is an exact multiple of the frame rate. IOW, 1 frame 1 pixel of movement, 1 frame 2 pixels of movement, and so on”
I think that is the issue combined with a cinematography issue that he also mentions: “One basic rule of thumb that almost always works is the “Seven Second Rule.” If it takes 7 seconds for the key element in your scene to move from one side of the screen to the other your shot will probably work.”
Does this make sense? I think I’m getting noticeable judder because of the type of imagery I’m using. If it were footage of a figure walking around in different directions or something less directional and constant, I don’t think I would be having this trouble.
As I mentioned, I have to animate the speed over time between 200% stretch and 100%. I’ve resorted to playing with motion blurs, which so far I haven’t gotten perfect. Is there another workflow you would suggest? Maybe use timewarp instead of time remapping? Real Smart Motion Blur?
Thanks for any input!!
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